package main

import . "fmt"
import . "strings"

func main() {
	var s string
	Scan(&s)
	for _, ch:=range s {
		cnt:=Count(s, string(ch))
		if cnt>2{
			Println("Impossible")
			return
		} else if cnt==1 {
			s += string(ch)
		}
	}
	if len(s) != 14 {
		Println("Impossible")
	} else {
		Println(s[13:14])
	}
}